Screen size calculator

Free Screen Size Calculator

Free screen size calculator. Enter aspect ratio + any one of diagonal, width, or height and the tool computes the other two in inches and centimeters. Ideal for monitor, TV, or laptop shopping.

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Screen Size Calculator

Pick an aspect ratio, then enter a diagonal, width, or height. The tool resolves the other two dimensions in inches and centimeters.

Pick your aspect ratio, then type a diagonal OR width OR height. The other two fill in instantly, in both inches and centimeters. Area is also calculated so you can compare the visible surface of two TVs or monitors.
Diagonal
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Width
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Height
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Visible area
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Tip: TV manufacturers advertise the diagonal in inches, but what actually matters for viewing distance is the width. A 55" 16:9 TV is 48" wide — very different from a 55" 21:9 ultrawide.
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Screen Size Calculator is a free, browser-based screen testing tool that runs the full check instantly in your web browser.

  • Cost: Free, no signup
  • Install: None — runs in the browser
  • Privacy: Runs locally, no uploads
  • Platforms: Windows, macOS, Linux, Android, iOS
  • Time: Under a minute

Why You Need More Than the Diagonal

TV and monitor marketing leads with the diagonal — "55-inch TV", "27-inch gaming monitor" — because it's one memorable number. But the diagonal alone doesn't tell you whether the screen fits your space or compares meaningfully to another product. A 55-inch 16:9 TV is 48 inches wide and 27 inches tall. A 55-inch 21:9 ultrawide monitor is 51 inches wide and 22 inches tall. Same diagonal, very different real estate on your desk or wall.

How The Math Works

Every screen is a rectangle with a fixed aspect ratio (width:height). If you know the aspect ratio and any one of diagonal, width, or height, basic trigonometry solves the other two:

  • From diagonal: width = diagonal × (aspect_w / √(aspect_w² + aspect_h²))
  • From width: height = width × (aspect_h / aspect_w), then diagonal = √(width² + height²)
  • From height: mirror of above

The calculator runs this live as you type and converts both ways between inches and centimeters.

Visible Area Is The Real Comparison

Two TVs with the same diagonal but different aspect ratios display different amounts of content. Visible area (width × height) is the best single number for "how much screen you actually get." A 27-inch 16:9 monitor has 311 square inches of screen. A 32-inch 16:9 monitor has 438 — about 40% more. A 34-inch 21:9 ultrawide has 424 — nearly the same area as the 32-inch flat panel but much wider and shorter.

Fitting A TV To A Space

Before ordering a new TV, measure the wall or cabinet width you have. Use this calculator to confirm the advertised diagonal fits. A "75-inch TV" is 65.4 inches wide (for 16:9) — it might not fit a 60-inch-wide media stand. Also factor in the TV bezel (usually +0.5 to +2 inches on each side) and any stand or wall-mount hardware.

Screen Size Calculator FAQ

Common screen size calculator questions

How wide is a 55-inch TV?

A 55-inch 16:9 TV is 47.9 inches wide and 27.0 inches tall (121.7 cm x 68.6 cm). A 55-inch 21:9 ultrawide is 50.6 inches wide and 21.7 inches tall.

Is screen size measured diagonally?

Yes. All TV and monitor sizes advertised (e.g. 27-inch, 55-inch) are the length of the visible diagonal, measured corner to corner.

How do I convert screen diagonal to width?

Multiply diagonal by aspect_w / sqrt(aspect_w^2 + aspect_h^2). For 16:9 that factor is 16/sqrt(337) ≈ 0.8716. So 55 inch diagonal * 0.8716 = 47.94 inches wide.

What aspect ratio is my TV?

Almost all TVs since 2007 are 16:9. Recent ultrawide monitors are 21:9. Phones in portrait are typically 9:16 or 9:19.5.

Related guide Monitor Gamma Test: Check Gamma 2.2 and Fix Washed-Out or Too-Dark Screens →

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